Department of Chemistry

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The Latest Research Items

Microfluidic Mass Spec Detection

Biotherapeutics, monoclonal antibodies, mAbs, in particular, represent a multi-billion dollar industry that continues to expand. In order to be used as a therapeutic agent the biomolecule must be rigorously characterized in order to ensure safety, efficacy, and potency. However, the size and complexity of mAbs makes this a challenging task. In work published in Analytical Chemistry, researchers in the Ramsey Group describe an integrated microfluidic capillary electrophoresis-electrospray ionization, CE-ESI, device for the separation of intact monoclonal antibody charge variants with online mass spectrometric, MS, identification.

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Schematic for CE-ESI devices with a 23 cm separation channel with an enlarged image of the asymmetric turn tapering. Red channels indicate an APS coating while black channels indicate an APS-PEG450 coating. S: sample reservoir; B: background electrolyte reservoir; SW: sample waste reservoir; EO: electroosmotic pump reservoir.

The surface chemistry utilized in the device channels suppressed the electroosmotic flow and prevented analyte adsorption, eliminating the need for complex background electrolyte additives. The microfluidic ESI interface proved vital to the successful ionization and resulting MS analysis by maintaining fluid flow to generate stable ESI. The effectiveness of the technique was demonstrated with the determination of five charge variants in the separation of Infliximab with an additional two mAbs analyzed to show the general applicability of the approach.

 

Quinary Structure Modulates Protein Stability

Protein quinary interactions organize the cellular interior and its metabolism. Although the interactions stabilizing secondary, tertiary, and quaternary protein structure are well defined, details about the protein–matrix contacts that compose quinary structure remain elusive. This gap exists because proteins function in the crowded cellular environment, but are traditionally studied in simple buffered solutions.

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Researchers in the Pielak Group use NMR-detected H/D exchange to quantify quinary interactions between the B1 domain of protein G and the cytosol of Escherichia coli. In their work, published in PNAS, the group demonstrates that a surface mutation in this protein is 10-fold more destabilizing in cells than in buffer, a surprising result that firmly establishes the significance of quinary interactions. Remarkably, the energy involved in these interactions can be as large as the energies that stabilize specific protein complexes. These results will drive the critical task of implementing quinary structure into models for understanding the proteome.

 

Charge Transfer in NaCl

The phenomenon of ion pairing in aqueous solutions is of widespread importance in chemistry and physics, and charge transfer between the ions is fundamental to understanding the behavior of aqueous ionic solutions. At the same time, it is of significant challenge to describe the charge transfer behavior using popular density functional theory, DFT, calculations in practice because of approximated exchange-correlation effects of electrons.

Journal Cover

In work published as a Frontiers Article and also as the cover article in Chemical Physics Letter, the group of Professor Yosuke Kanai shows how advanced quantum Monte Carlo, QMC, calculation is used to accurately quantify the charge transfer behavior in the NaCl dimer. Accurate electron density is obtained from the so-called reptation Monte Carlo approach, and influence of fermion nodes of the many-body wavefunction on the charge transfer behavior was discussed in detail. It is anticipated that the QMC approach will be of great importance for investigating a wide range of the charge transfer phenomena for which present-day DFT calculations are not reliable.

 

Potential Pancreatic Cancer Treatment

Parenteral and oral routes have been the traditional methods of administering cytotoxic agents to cancer patients. Unfortunately, the maximum potential effect of these cytotoxic agents has been limited because of systemic toxicity and poor tumor perfusion. In an attempt to improve the efficacy of cytotoxic agents while mitigating their side effects, researchers in the DeSimone Group, in a broadly collaborative work, have developed modalities for the localized iontophoretic delivery of cytotoxic agents. As described in Science Translational Medicine, these iontophoretic devices were designed to be implanted proximal to the tumor with external control of power and drug flow.

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Device therapy Compared to a control (left), mice treated with a chemotherapy drug using the device experienced significant growth reduction as confirmed by the lack of brown staining for a marker of tumor growth.

"Surgery to remove a tumor currently provides the best chance to cure pancreatic cancer," said DeSimone, Chancellor's Eminent Professor of Chemistry here at UNC, and William R. Kenan, Jr. Distinguished Professor of Chemical Engineering at NC State University. "However, often a diagnosis comes too late for a patient to be eligible for surgery due to the tendency of the tumors to become intertwined with major organs and blood vessels." James Byrne, a member of the DeSimone Group, led the research by constructing the device and examining its ability to deliver chemotherapeutic drugs effectively to pancreatic cancer tumors, as well as two types of breast cancer tumors. Depending on the tumor type, the new device can be used either internally after a minimally invasive surgery to implant the device's electrodes directly on a tumor, or externally to deliver drugs through the skin. Overall, these devices have potential paradigm shifting implications for the treatment of pancreatic, breast, and other solid tumors.

 

Hybrid Thermal Assembly Technique

Over the past decade, thermoplastics have been used as alternative substrates to glass and Si for microfluidic devices because of the diverse and robust fabrication protocols available for thermoplastics that can generate high production rates of the desired structures at low cost and with high replication fidelity, the extensive array of physiochemical properties they possess, and the simple surface activation strategies that can be employed to tune their surface chemistry appropriate for the intended application. While the advantages of polymer microfluidics are currently being realized, the evolution of thermoplastic-based nanofluidic devices is fraught with challenges. One challenge is assembly of the device, which consists of sealing a cover plate to the patterned fluidic substrate.

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Typically, channel collapse or substrate dissolution occurs during assembly, making the device inoperable resulting in low process yield rates. Now, in an article published in Lab on a Chip as a "Hot Article," researchers in the Soper Group report a low temperature hybrid assembly approach for the generation of functional thermoplastic nanofluidic devices with high process yield rates, >90%, and with a short total assembly time of only sixteen minutes. The functionality of the assembled devices was demonstrated by studying the stretching and translocation dynamics of dsDNA in the enclosed thermoplastic nanofluidic channels.